As is known, some digital data service (hereinafter "DDS") receivers are arranged to receive a 2-binary, 1-quaternary (hereinafter "2B1Q")-coded signal. The 2B1Q signal is a 4-level signal, with allowed signal levels of +3 volts (corresponding to a logical value of 10), +1 volts (corresponding to a logical value of 11), -1 volts (corresponding to a logical value of 01), and -3 volts (corresponding to a logical value of 00).
As is known, typically the 2B1Q-coded DDS signal is distorted by the telephone line providing the signal to the receiver. The distortion is caused by the capacitance of the telephone line acting to smooth-out and round-off the multi-level pulses, thus causing time delay, phase delay, and attenuation of the voltage levels.
To allow operation over long ranges, therefore, this distortion must be corrected. As a result, an equalizer is needed to boost the signal level and remove the frequency and phase error.